docs: def Turner_Wallis(x, rhol, rhog, mul, mug):
      r'''Calculates void fraction in two-phase flow according to the model of 
      [1]_, as given in [2]_ and [3]_.
  
      .. math::
          \alpha = \left[1 + \left(\frac{1-x}{x}\right)^{0.72}\left(\frac{\rho_g}
          {\rho_l}\right)^{0.4}\left(\frac{\mu_l}{\mu_g}\right)^{0.08}
          \right]^{-1}
          
      Parameters
      ----------
      x : float
          Quality at the specific tube interval []
      rhol : float
          Density of the liquid [kg/m^3]
      rhog : float
          Density of the gas [kg/m^3]
      mul : float
          Viscosity of liquid [Pa*s]
      mug : float
          Viscosity of gas [Pa*s]
  
      Returns
      -------
      alpha : float
          Void fraction (area of gas / total area of channel), [-]
  
      Notes
      -----
      [1]_ has not been reviewed. However, both [2]_ and [3]_ present it the
      same way, if slightly differently rearranged.
  
      Examples
      --------
      >>> Turner_Wallis(.4, 800, 2.5, 1E-3, 1E-5)
      0.8384824581634625
  
      References
      ----------
      .. [1] J.M. Turner, G.B. Wallis, The Separate-cylinders Model of Two-phase 
         Flow, NYO-3114-6, Thayer's School Eng., Dartmouth College, Hanover, New 
         Hampshire, USA, 1965.
      .. [2] Xu, Yu, and Xiande Fang. "Correlations of Void Fraction for Two-
         Phase Refrigerant Flow in Pipes." Applied Thermal Engineering 64, no. 
         1-2 (March 2014): 242–51. doi:10.1016/j.applthermaleng.2013.12.032. 
      .. [3] Dalkilic, A. S., S. Laohalertdecha, and S. Wongwises. "Effect of 
         Void Fraction Models on the Two-Phase Friction Factor of R134a during 
         Condensation in Vertical Downward Flow in a Smooth Tube." International 
         Communications in Heat and Mass Transfer 35, no. 8 (October 2008): 
         921-27. doi:10.1016/j.icheatmasstransfer.2008.04.001.
      '''
      return (1 + ((1-x)/x)**0.72 * (rhog/rhol)**0.4 * (mul/mug)**0.08)**-1